Image processing method, image processing apparatus, and image processing program

ABSTRACT

In the image processing apparatus, Input transform into an input color space is performed on input image data; After the input transform, transform processing of transforming chroma or chromaticity of the input image data or chroma or chromaticity in the input color space is performed so as to reduce a difference between a space of chroma or chromaticity of the input image data and a space of chroma or chromaticity in the input color space to acquire transformed image data; and Output transform into an output color space is performed on the transformed image data using a three-dimensional lookup table including inverse transform processing of returning the chroma or chromaticity of the transformed image data to the chroma or chromaticity of the input image data to acquire output image data.

BACKGROUND OF THE INVENTION

This invention relates to an image processing method, an imageprocessing apparatus, and an image processing program, and moreparticularly, to an image processing method and an image processingapparatus which can improve the accuracy of color space transform ofimage data having a color space of a wide dynamic range, particularly,the accuracy of the color space transform using a three-dimensionallookup table (hereinafter, also referred to as “3DLUT”), an imageprocessing program for causing a computer to execute the imageprocessing method, and a computer-readable recording medium having theimage processing program recorded thereon.

Scene-referred image representations having exact color information ofimaged objects and sights are used for the purpose of exact colorreproduction and are used as a reference of a captured image in colormanagement. For example, the Academy of Motion Picture Arts and Sciences(AMPAS) defined a scene-referred wide dynamic range image color space(Academy Color Encoding Specification (ACES) color space), which isdescribed in Non-Patent Document 1 (Specification S-2008-001, AcademyColor Encoding Specification (ACES), The Academy of Motion Picture Artsand Sciences, Science and Technology Council, Image InterchangeFramework Subcommittee, Version 1.0, Aug. 12, 2008) in color managementfor movie production and uses it as a reference for matching colors ofimages captured with various cameras.

The ACES color space has a very wide dynamic range as described above,and image data of pixels is expressed as floating point numbers. At thetime of image transform or the like, it is necessary to deal with theimage data of a wide dynamic range as an input.

Output-referred image data is obtained by performing reference renderingtransform (RRT), which is called rendering, on the image data in theACES color space. The rendering (RRT) serves as contrast or colortransform according to observation environments (brightness or colortone of a light source) and color transform for desirable reproduction(memory colors such as desirable flesh color, sky, and green). In thestandard of AMPAS, the rendering (RRT) is defined by complicatednumerical expressions. However, in an actual color transform system,these complicated numerical expressions can be hardly used without anychange and thus need to be replaced with a three-dimensional lookuptable (3DLUT).

The 3DLUT is a table in which output values Ro, Go, and Bo can bearbitrarily set for combinations of input values Ri, Gi, and Bi, wherethe input values can be set to be discrete and an input between thediscrete values can be obtained from preceding and subsequent valuesthereof by interpolation.

An example of the table indicating the 3DLUT is shown in Table 1.

TABLE 1 Ri Gi Bi Ro Go Bo 0 0 0 0.12 0.08 0.01 0 0 8 0.22 0.07 6.45 0 016 0.31 0.05 15.23 . . . . . . . . . . . . . . . . . . 0 8 0 0.21 11.251.35 . . . . . . . . . . . . . . . . . . 256  256 256 238.12 248.35255.56

As the input values of the 3DLUT, combinations of R, G, and B of thesame values with equal divisions are widely used from the viewpoint ofconvenience of operation. When the input values of the 3DLUT areexpressed in a three-dimensional space of R, G, and B, the input valuescan be expressed as a grid-like cube illustrated in FIG. 11.

The 3DLUT illustrated in FIG. 11 covers a space of combination of all R,G, and B values in a range of 0 to 256.

In the case where transform from a color space of a wide dynamic rangesuch as the ACES color space is performed using the 3DLUT, the range tobe covered with the 3DLUT is broadened and thus high-accuracy transformcannot be performed without taking a large number of coordinates (gridpoints) of the input values designated discretely in the 3DLUT.

Accordingly, in the case where an image having a wide dynamic range is atarget of transform, since outdoor sunlight is equal to or greater than10000 cd/m², moonlight is approximately 0.01 cd/m², and a dynamic rangeis 6 (=Log₁₀(10000/0.01)), it is thus necessary to apply a lookup table(hereinafter, also referred to as LUT) covering this range. In general,since input values of an LUT are values of equal-interval steps,10⁶=1000000 input values are required to cover the wide dynamic range,and besides, there is a problem in that a resolution is roughened in adark area, and the human perception has a Log function relationship forbrightness (Weber-Fechner's Law). Therefore, a method of implementing anLUT after performing Log transform on image data having linearbrightness is suitably used. By applying the 3DLUT having input gridpoints of equal intervals to the data subjected to the Log transform, itis possible to approximate the transform with data, which is discretizedby distribution for human perception.

Therefore, in a video transform architecture (a logical structure ofcomputer hardware performing an image transform processing) proposed bythe AMPAS, the 3DLUT is adopted to transform from the ACES color spaceinto a color space for an output device.

FIG. 12 illustrates an image transform processing system 120 constructedon the basis of the video transform architecture proposed by the AMPAS.

In the image transform processing system 120 illustrated in FIG. 12,first, a camera image (video) 124 captured with a digital camera as aninput device is input to a data input unit 122 and is acquired in theimage transform processing system 120.

Image data of the camera image 124 (the color space of the digitalcamera) is transformed through input device transform (IDT) 128 or thelike in an input transform unit 126 into image data of an ACES colorspace (input color space) 132 that is independent from the input device.

The image data transformed into the ACES color space 132 is subjected toediting/processing such as color adjustment in the ACES color space 132in a color adjusting unit 130, is then transformed into an output colorspace (Output Color Encoding Specification (OCES) color space (notillustrated)) which is a color space common to the ACES color space 132through reference rendering transform (RRT) 136 in an output transformunit 134, and is then transformed into image data of an output image 142displayed on a display device 140 such as a digital projector throughoutput device transform (ODT) 138.

In the image transform processing system 120 illustrated in FIG. 12, a3DLUT is adopted to the combination of the RRT 136 and the ODT 138 inthe output transform unit 134.

The 3DLUT used in the output transform unit 134 can be a 3DLUT 46applied so as to entirely cover a color space 44 which is illustrated inFIG. 3B and which is the ACES color space 132 transformed through theIDT 128.

SUMMARY OF THE INVENTION

However, in the image transform processing system 120 illustrated inFIG. 12, when color transform such as the rendering (RRT 136) of a widedynamic range in the ACES color space 132 or the like is expressed bythe three-dimensional lookup table (3DLUT 46) as illustrated in FIG. 3B,data between neighboring grid points is calculated by linearinterpolation, and thus there is a problem in that as the nonlinearityof the color transform becomes stronger, the accuracy of the colortransform degrades, if the number of grid points is not increased.Particularly, since the human perception is sensitive to an error in thevicinity of gray, there is a problem in that color undulation, tonejump, or the like is observed.

The grid points of the 3DLUT are generally 17³, 33³, 66³, and the like,and when the number of grid points is increased to enhance the accuracyof color transform, there is a problem in that the amount of databecomes enormous or the processing speed of the color transformdecreases.

The invention is made to solve the above-mentioned problems in the priorart and an object thereof is to provide an image processing method andan image processing apparatus that can improve the accuracy of colorspace transform, particularly, color space transform using athree-dimensional lookup table, of image data having a color space of awide dynamic range and particularly, can increase the density of gridpoints in the vicinity of gray without increasing the number of gridpoints of the three-dimensional lookup table, an image processingprogram causing a computer to execute the image processing method, and acomputer-readable recording medium having the image processing programrecorded thereon.

To attain the above object, the present invention provides an imageprocessing method of sequentially performing input transform into aninput color space and output transform into an output color space oninput image data to transform the input image data into output imagedata, comprising:

after the input transform, performing transform processing oftransforming chroma or chromaticity of the input image data or chroma orchromaticity in the input color space so as to reduce a differencebetween a space of chroma or chromaticity of the input image data and aspace of chroma or chromaticity in the input color space so that thespace of chroma or chromaticity of the input image data effectively usesthe space of chroma or chromaticity in the input color space to acquiretransformed image data; and

in the output transform, performing image processing of transforming thetransformed image data into the output image data using athree-dimensional lookup table including inverse transform processing ofreturning the chroma or chromaticity of the transformed image data tothe chroma or chromaticity of the input image data.

Also, the present invention provides an image processing method ofsequentially performing input transform into an input color space, coloradjustment, and output transform into an output color space on inputimage data of an input device to transform the input image data intooutput image data of an output device, comprising:

after the input transform, performing transform processing oftransforming chroma of the input image data or chroma in the input colorspace so as to reduce a difference between a space of chroma of theinput image data and a space of chroma in the input color space so thatthe space of chroma of the input image data effectively uses the spaceof chroma in the input color space to acquire transformed image data;and

in the output transform, performing inverse transform processing ofreturning the chroma of the transformed image data to the chroma of theinput image data and image processing of transforming the transformedimage data into the output image data.

Also, the present invention provides an image processing method ofsequentially performing input transform into an input color space andinteger encoding on input image data, transmitting the integer-encodedtransformed image data, and transforming the transmitted transformedimage data into output image data in an output color space, comprising:

after the input transform, performing transform processing oftransforming chroma of the input image data or chroma in the input colorspace so as to reduce a difference between a space of chroma of theinput image data and a space of chroma in the input color space so thatthe space of chroma of the input image data effectively uses the spaceof chroma in the input color space to acquire transformed image data;and

in the output transform, performing inverse transform processing ofreturning the chroma of the transformed image data to the chroma of theinput image data and image processing of transforming the transformedimage data into the output image data.

Also, the present invention provides an image processing apparatuscomprising:

an input transform unit configured to perform input transform into aninput color space on input image data;

a chroma/chromaticity optimizing unit configured to perform transformprocessing of transforming chroma or chromaticity of the input imagedata or chroma or chromaticity in the input color space so as to reducea difference between a space of chroma or chromaticity of the inputimage data and a space of chroma or chromaticity in the input colorspace so that the space of chroma or chromaticity of the input imagedata effectively uses the space of chroma or chromaticity in the inputcolor space to acquire transformed image data, after the inputtransform; and

an output transform unit configured to perform output transform into anoutput color space on the transformed image data to acquire output imagedata,

wherein in the output transform, the output transform unit performsimage processing of transforming the transformed image data into theoutput image data using a three-dimensional lookup table includinginverse transform processing of returning the chroma or chromaticity ofthe transformed image data to the chroma or chromaticity of the inputimage data.

Also, the present invention provides an image processing apparatuscomprising:

an input transform unit configured to perform input transform into aninput color space on input image data of an input device;

a chroma/chromaticity optimizing unit configured to perform transformprocessing of transforming chroma or chromaticity of the input imagedata or chroma or chromaticity in the input color space so as to reducea difference between a space of chroma or chromaticity of the inputimage data and a space of chroma or chromaticity in the input colorspace so that the space of chroma or chromaticity of the input imagedata effectively uses the space of chroma or chromaticity in the inputcolor space to acquire transformed image data, after the inputtransform;

a color adjusting unit configured to perform color adjustment on thetransformed image data acquired by the chroma/chromaticity optimizingunit; and

an output transform unit configured to perform output transform into anoutput color space of an output device on the transformed image datasubjected to color adjustment by the color adjusting unit to acquireoutput image data,

wherein in the output transform, the output transform unit performsinverse transform processing of returning the chroma or chromaticity ofthe transformed image data subjected to color adjustment by the coloradjusting unit to the chroma or chromaticity of the input image data andimage processing of transforming the transformed image data subjected tocolor adjustment by the color adjusting unit into the output image data.

Also, the present invention provides an image processing apparatuscomprising:

an input transform unit configured to perform input transform into aninput color space on input image data;

a chroma/chromaticity optimizing unit configured to perform transformprocessing of transforming chroma or chromaticity of the input imagedata or chroma or chromaticity in the input color space so as to reducea difference between a space of chroma or chromaticity of the inputimage data and a space of chroma or chromaticity in the input colorspace so that the space of chroma or chromaticity of the input imagedata effectively uses the space of chroma or chromaticity in the inputcolor space to acquire transformed image data, after the inputtransform;

an integer encoding unit configured to perform integer encoding on thetransformed image data acquired by the chroma/chromaticity optimizingunit; and an output transform unit configured to perform outputtransform into an output color space on the transformed image datasubjected to integer encoding by the integer encoding unit to acquireoutput image data,

wherein in the output transform, the output transform unit performsinverse transform processing of returning the chroma or chromaticity ofthe transformed image data to the chroma or chromaticity of the inputimage data and image processing of transforming the transformed imagedata into the output image data.

Also, the present invention provides a non-transitory computer-readablerecording medium having recorded thereon an image processing program forcausing a computer to execute respective steps of the image processingmethod according to above.

According to the invention, the constitution described above can improvethe accuracy of color space transform of an image data having a colorspace of a wide dynamic range, particularly, color space transform usinga three-dimensional lookup table and, particularly, can increase thedensity of grid points in the vicinity of gray without increasing thenumber of grid points of the three-dimensional lookup table used inimage-encoding for image processing or image transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a configuration of an imageprocessing apparatus that performs an image processing method accordingto the invention.

FIG. 2 is a block diagram schematically illustrating a first embodimentof the configuration of the image processing apparatus that performs theimage processing method according to the invention.

FIGS. 3A and 3B are conceptual diagrams respectively illustrating theimage processing method according to the invention and the conventionalimage processing method.

FIG. 4 is a flowchart illustrating an example of a process flow of theimage processing method according to the invention.

FIG. 5 is a block diagram schematically illustrating a second embodimentof the configuration of the image processing apparatus that performs theimage processing method according to the invention.

FIG. 6 is a block diagram schematically illustrating a third embodimentof the configuration of the image processing apparatus that performs theimage processing method according to the invention.

FIG. 7 is a conceptual diagram illustrating a state of transforming afirst color space composed of brightness and chromaticity into alow-chromaticity color space in which the chromaticity of the firstcolor space has decreased.

FIG. 8 is a block diagram schematically illustrating a fourth embodimentof the configuration of the image processing apparatus that performs theimage processing method according to the invention.

FIG. 9 is a conceptual diagram illustrating a state of transforming asecond color space composed of brightness, chroma, and hue into alow-chroma color space in which the chroma of the second color space hasdecreased.

FIG. 10 is a block diagram schematically illustrating a fifth embodimentof the configuration of the image processing apparatus that performs theimage processing method according to the invention.

FIG. 11 is a perspective view schematically illustrating athree-dimensional lookup table as a grid-like cube.

FIG. 12 is a block diagram illustrating the conventional image transformprocessing system.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an image processing method, an image processing apparatus,an image processing program, and a recording medium according to theinvention will be described in detail with reference to exemplaryembodiments illustrated in the accompanying drawings.

FIG. 1 is a block diagram illustrating a configuration of an imageprocessing apparatus that performs an image processing method accordingto the invention. The image processing apparatus 80 illustrated in thedrawing sequentially performs input transform into an input color spaceand output transform into an output color space on input image data totransform the input image data into output image data, and includes aninput transform unit 82, a chroma/chromaticity optimizing unit 84, andan output transform unit 86.

The input transform unit 82 performs transform (input transform) oninput image data into an input color space such as an ACES color spaceof the AMPAS.

After the input transform by the input transform unit 82, thechroma/chromaticity optimizing unit 84 performs transform processing oftransforming (optimizing) chroma or chromaticity of the input image dataor chroma or chromaticity in the input color space so as to reduce adifference between a space of chroma or chromaticity of the input imagedata captured with an input device such as a digital camera and a spaceof chroma or chromaticity in the input color space having a wide dynamicrange such as the ACES color space 20 so that a space of chroma orchromaticity of the input image data captured with an input deviceeffectively uses the space of chroma or chromaticity in the input colorspace having a wide dynamic range, that is, so as to match the space ofchroma or chromaticity used for actual image data, and thus acquirestransformed image data.

The output transform unit 86 performs transform (output transform) onthe transformed image data acquired by the chroma/chromaticityoptimizing unit 84 into the output color space to acquire output imagedata. In addition, in the output transform, the output transform unit 86performs image processing of transforming the transformed image datainto the output image data using a three-dimensional lookup table(3DLUT) including inverse transform processing of returning the chromaor chromaticity of the transformed image data to the chroma orchromaticity of the input image data.

In a first embodiment of the invention, after the input transform by theinput transform unit 82, the chroma/chromaticity optimizing unit 84performs transform processing of increasing chroma of the input imagedata to acquire transformed image data.

Then, in the output transform, the output transform unit 86 performsimage processing of transforming the transformed image data into theoutput image data using a 3DLUT including inverse transform processingof decreasing the amount of chroma increased in the transformed imagedata to return the chroma of the transformed image data to the chroma ofthe input image data.

In a second embodiment of the invention, after the input transform bythe input transform unit 82, the chroma/chromaticity optimizing unit 84performs transform processing of transforming the input image data inthe input color space into image data in a high-chroma color space inwhich chroma has increased with respect to the input color space toacquire transformed image data.

Then, in the output transform, the output transform unit 86 performsimage processing of transforming the transformed image data to theoutput image data using a 3DLUT including inverse transform processingof inversely transforming the transformed image data in the high-chromacolor space into the input image data in the input color space.

In a third embodiment of the invention, after the input transform by theinput transform unit 82, the chroma/chromaticity optimizing unit 84performs transform processing of transforming the input image data inthe input color space into image data in a first color space composed ofbrightness and chromaticity and transforming the first color space to alow-chromaticity color space in which the chromaticity of the firstcolor space has decreased to acquire transformed image data.

Then, in the output transform, the output transform unit 86 performsimage processing of transforming the transformed image data into theoutput image data using a 3DLUT including inverse transform processingof inversely transforming the low-chromaticity color space into thefirst color space and inversely transforming the image data in theinversely-transformed first color space into the input image data in theinput color space.

In a fourth embodiment of the invention, after the input transform bythe input transform unit 82, the chroma/chromaticity optimizing unit 84performs transform processing of transforming the input image data inthe input color space into image data in a second color space composedof brightness, chroma, and hue and transforming the second color spaceto a low-chroma color space in which the chroma of the second colorspace has decreased to acquire transformed image data.

Then, in the output transform, the output transform unit 86 performsimage processing of transforming the transformed image data into theoutput image data using a 3DLUT including inverse transform processingof inversely transforming the low-chroma color space into the secondcolor space and inversely transforming the image data in theinversely-transformed second color space into the input image data inthe input color space.

Next, the general operation of the image processing apparatus 80 will bedescribed below with reference to the image processing method accordingto the invention.

In the image processing apparatus 80, transform (input transform) of theinput image data into the input color space is performed by the inputtransform unit 82.

Subsequently, by the chroma/chromaticity optimizing unit 84, transformprocessing of transforming the chroma or chromaticity of the input imagedata or the chroma or chromaticity of the input color space is performedso as to reduce a difference between a space of chroma or chromaticityof the input image data and a space of chroma or chromaticity in theinput color space so that the space of chroma or chromaticity of theinput image data effectively uses the space of chroma or chromaticity inthe input color space, and thus transformed image data is acquired.

Then, by the output transform unit 86, image processing of transformingthe transformed image data into the output image data is performed usinga 3DLUT including inverse transform processing of returning the chromaor chromaticity of the transformed image data to the chroma orchromaticity of the input image data.

In this way, in the image processing apparatus 80, by reducing thedifference between a space of chroma or chromaticity of the input imagedata and a space of chroma or chromaticity in the input color space sothat the space of chroma or chromaticity of the input image dataeffectively uses the space of chroma or chromaticity in the input colorspace and inputting the resultant input image data to the 3DLUT, it ispossible to improve utilization rate of data of the respective gridpoints of the 3DLUT without increasing the number of grid points of the3DLUT. Therefore, it is possible to increase the density of the gridpoints in the vicinity of gray and thus to improve the accuracy of thecolor space transform of image data having a color space of a widedynamic range using the 3DLUT.

That is, by reducing the difference between the color space of the inputimage data and the input color space, it is possible to improve theutilization rate of the input color space and thus to improve theaccuracy of transform.

First to fourth embodiments of the image processing apparatus thatperforms the image processing method according to the invention will bedescribed below.

First, an image processing apparatus according to the first embodimentwill be described.

FIG. 2 is a block diagram schematically illustrating the firstembodiment of the configuration of the image processing apparatus thatperforms the image processing method according to the invention.

As illustrated in FIG. 2, the image processing apparatus 10 is basicallyconstructed on the basis of the color transform architecture of theAMPAS and includes a data input unit 12, an input transform unit 14, achroma increase processing unit 16, a color adjusting unit 18, an outputtransform unit 20, and a display device 22. The input transform unit 14includes an IDT 26 and the output transform unit 20 includes a chromadecrease processing unit 30, an RRT 32, and an ODT 34.

The data input unit 12 is a unit to which camera image data 24 capturedwith a digital camera or the like as an input device is input and bywhich the camera image data 24 is acquired in the image processingapparatus 10. The camera image data 24 acquired by the data input unit12 is input to the input transform unit 14.

The input transform unit 14 includes the IDT 26, like the IDT 128 of theimage transform processing system 120 illustrated in FIG. 12 based onthe color transform architecture of the AMPAS and transforms (inputtransforms) the camera image data 24 into image data in the ACES colorspace (input color space) 28 of the AMPAS, which is then subjected toediting/processing such as color adjustment by the color adjusting unit18.

Similarly to the IDT 128 illustrated in FIG. 12, the IDT 26 transformsthe camera image data 24 (the color space of the digital camera or thelike) captured with the input device such as a digital camera into theimage data in the ACES color space 28 which is the common color space ofthe input defined as a scene-referred color space and which isindependent from the input device such as a digital camera.

The input transform unit 14 may correct the image data, which has beentransformed into image data in the ACES color space 28 by the IDT 26,depending on the individual difference of input devices.

By doing so, since plural pieces of camera image data 24 captured withvarious input devices such as plural different digital cameras aretransformed into plural pieces of image data in the ACES color space 28defined as a scene-referred color space, the plural pieces of inputimage data of the same scene are transformed into plural pieces of imagedata having the same color.

Accordingly, even plural pieces of camera image data captured withvarious input devices such as plural digital cameras of different makersor types can be transformed into plural pieces of image data in the ACEScolor space 28 which are matched with high accuracy.

The chroma increase processing unit 16 is a characterized part of theinvention, is an example of the chroma/chromaticity optimizing unit 84illustrated in FIG. 1, and performs transform processing of increasingthe chroma (chroma UP) of the image data in the ACES color space 28transformed by the IDT 26 to acquire transformed image data.

As illustrated in FIG. 3A, a color space 40 in which chroma hasincreased with respect to an original color space 44 illustrated in FIG.3B is defined, and a 3DLUT 42 which has the same number of grid pointsas the conventional three-dimensional lookup table (3DLUT) 46 defined soas to entirely cover the original color space 44 illustrated in FIG. 3Bis defined so as to be applied to the central area of the color space40.

Here, the input color space 40 used in the invention is a color spacehaving the same width in the gray (brightness) and a greater width inthe hue direction as compared to the original color space 44. That is,as compared to the original color space 44, the input color space 40extends in the hue direction and thus the chroma increases, but does notextend and is constant in the brightness direction and thus thebrightness does not vary.

As described above, the 3DLUT 46 illustrated in FIG. 3B is a 3DLUT usedin the output transform unit 134 illustrated in FIG. 12, the 3DLUT 42 ofthe invention illustrated in FIG. 3A is a 3DLUT used in the outputtransform unit 20 to be described later, and the both of 3DLUT 46 and3DLUT 42 have the same number of grid points, but the 3DLUT 42 of theinvention is different from the conventional 3DLUT 46, in that the 3DLUTof the invention includes processing of decreasing the chroma increasedby the chroma increase processing unit 16 to return the chroma to theoriginal chroma.

In this way, by performing color transform from the color space of whichthe chroma has increased without changing the number of grid points(size) of the 3DLUT 42 of the invention, a disadvantage that transformof an area having high chroma cannot be performed arises. However, inconsideration of a color space of a wide dynamic range such as the ACEScolor space 28 having, for example, a color space of a range of −4 to +2in terms of Log, a high-chroma color is, for example, a color of RGBcombination (−4, −3, +1) and is equivalent to a color of brightnesscombination (0.01%, 0.1%, 1000%) in terms of antilogarithm. A subjecthaving a color of such an extreme brightness is hardly present inreality.

Accordingly, when a 3DLUT having a limited number of grid points isused, it is effective to narrow the coverage in the chroma direction toa range present in real scenes and to exclude a high-chroma range notpresent in real scenes from the transform target of the 3DLUT.

That is, in the chroma increase processing in the chroma increaseprocessing unit 16, since the area to which the 3DLUT 42 illustrated inFIG. 3A is applied only has to cover the image data in the entirereproducible color space of the output image 38 of the display device 22to be described later, that is, the image data in the entire outputcolor space of the ODT 34 of the output transform unit 20, the outputcolor space of the ODT 34 can be inversely transformed so that theoutput color space is adjusted to be an area in the ACES color space 28.

Accordingly, the chroma increase processing that is performed by thechroma increase processing unit 16 is not particularly limited as longas it can be adjusted in this way.

For example, it is preferable that the chroma increase processing beperformed in a logarithmic (Log) color space using logarithmic (Log)transformed values of the input camera image data and thechroma-increased image data. The reason is that since in the invention,an image having a wide dynamic range is used as a target, it isnecessary to cover the wide dynamic range as described above, theresolution is roughened in a dark area, and the human perception ofbrightness has a Log function relationship.

In addition, the chroma increase processing by the chroma increaseprocessing unit 16 is preferably matrix transform processing and is morepreferably performed, for example, using an R (Red), G (Green), and B(Blue) matrix or a YCC matrix. The reason is that the matrix operationcan be performed as a simple operation, the chroma increase processingby the chroma increase processing unit 16 and the chroma decreaseprocessing by the chroma decrease processing unit 30 to be describedlater can be simply performed, the chroma decrease processing of theinverse transform processing can be easily applied to the 3DLUT, and theinterpolation of the grid points in the 3DLUT is linear transform andthus the accuracy of the simple linear transform is higher than that ofa combination with nonlinear transform.

Moreover, when the chroma increase processing is performed by the chromaincrease processing unit 16, it is preferable that the rate of increaseof chroma be changed depending on the distance of the input camera imagedata from gray, specifically, the distance of the image data from grayin the ACES color space 28 which is a common color space of the inputand into which the camera image data is transformed by the IDT 26. Thereason is that the human perception is sensitive to a difference in thevicinity of gray.

The rate of increase of chroma may be changed depending on YCC,brightness, or the like instead of changing the rate of increase ofchroma depending on the distance from gray.

A specific example of the chroma increase processing by the chromaincrease processing unit 16 will be described later.

Similarly to the color adjusting unit 130 in the ACES color space 132illustrated in FIG. 12, the color adjusting unit 18 is used to adjustcolors of an image, for example, colors of a scene, in the ACES colorspace 28, on the basis of a color adjustment parameter or the like. Forexample, in case of a video such as a movie, the color adjusting unit 18performs color adjustment for direction suitable to atmosphere of videocontents, stories, or scenes. Since the color adjusting unit 18transforms image data into color-adjusted image data in the ACES colorspace 28, the color space of the color-adjusted image data is also theACES color space 28. Here, in the color adjusting unit 18, transformsuch as the color adjustment is performed in the ACES color space 28 ina state where the chroma is increased. Since the transform such as thecolor adjustment by the color adjusting unit 18 is a transform in astate where the chroma is increased, it has an effect that even fineportions existing in a scene can be transformed.

The output transform unit 20 transforms (output transforms) thecolor-adjusted transformed image data in the ACES color space 28color-adjusted by the color adjusting unit 18 into output image data fordisplaying an output image 38 on a display screen of the display device22, and includes the chroma decrease processing unit 30, the RRT 32, andthe ODT 34 as described above.

The output transform unit 20 does not individually perform the chromadecrease processing by the chroma decrease processing unit 30, thetransform into the OCES color space by the RRT 32, and the output devicetransform by the ODT 34, but performs the three processings using asingle 3DLUT.

Since as the 3DLUT 42 illustrated in FIG. 3A, the 3DLUT of the outputtransform unit 20 covers only an area obtained by cutting out an areawhich is not present at all or hardly present in an actual scene on bothincreased (extended) sides of the color space 40 of which the chroma hasincreased (extended in the hue direction), the input of the 3DLUT iscoincide with grid points in the covered area.

The chroma decrease processing unit 30 decreases the chroma which hasbeen increased by the chroma increase processing unit 16, that is,decreases the chroma by the amount of chroma increased, to return thechroma to the original chroma.

The chroma decrease processing unit 30 performs processing of decreasingthe chroma in the output transform including the rendering transform(RRT) 32 using the 3DLUT 42 from the color space 40 of which the chromahas increased, as illustrated in FIG. 3A. Accordingly, since the chromaincreased by the chroma increase processing unit 16 is decreased by thechroma decrease processing unit 30, the total color transform resultdoes not change. In the color space 40 of which the chroma increased,the width of the space is not changed in the gray (brightness)direction, and accordingly, the transform of decreasing the chroma inthe color space 40 extended in only the hue direction before the RRT 32is expressed by the 3DLUT 42 and is applied thereto.

Here, the decrease of chroma (chroma DOWN) in the chroma decreaseprocessing unit 30 can be operated, for example, using Expression (1).

G _(ray)=(R _(i) +G _(i) +B _(i))/3

R _(o) =R _(i)−(R _(i) −G _(ray))*k

G _(o) =G _(i)−(G _(i) −G _(ray))*k

B _(o) =B _(i)−(B _(i) −G _(ray))*k

Here, R_(i), G_(i), and B_(i) are RGB input values (image data) of thechroma increase processing, R_(o), G_(o), and B_(o) are RGB outputvalues (image data) of the chroma decrease processing, G_(ray) is theaverage value of the RGB input values and is a value of gray, and k is achroma decrease coefficient (0 to 1), where 0 denotes no chroma decreaseand 1 denotes zero chroma representing gray.

On the other hand, when the decrease of chroma in the chroma decreaseprocessing unit 30 is expressed by Expression (1), the increase ofchroma (chroma UP) in the chroma increase processing unit 16 is given asthe inverse transform of the above and can be operated using Expression(2).

R _(o)=(R _(i) −G _(ray) *k)/(1−k)

G _(o)=(G _(i) −G _(ray) *k)/(1−k)

B _(o)=(Bi−G _(ray) *k)/(1−k)

Here, R_(i), G_(i), and B_(i) are RGB input values (image data) of thechroma increase processing, and R_(o), G_(o), and B_(o) are RGB outputvalues (image data) of the chroma decrease processing.

The operation of the chroma increase processing defined in this waypreferably uses an operation matrix to which Expression (2) is modified.

In addition, in the increase of chroma by the chroma increase processingunit 16, it is possible to change the distance from gray by changing thecoefficient k between a value more than 0 and a value less than 1.

Here, in the transform by the ODT 34 of the output transform unit 20,data of at least the entire area of the color space of the output deviceonly has to be expressed. Accordingly, when the color space of theoutput device is inversely transformed into the ACES color space 28 andenters not the entire ACES color space 28 but a predetermined areathereof, the value of the coefficient k can be calculated as a value ina range covering the predetermined area. The value of the coefficient kmay be calculated from the color space of the output device, but theinvention is not limited to this, and a preliminarily set value, forexample, 0.5, may be used.

Next, similarly to the RRT 136 illustrated in FIG. 12, the RRT 32performs rendering (editing/processing) and performs rendering transformof transforming into an output standard color space that is independentfrom the output device, for example, the OCES color space. Specificexample of the rendering includes adjustment of contrast of an outputimage and colors of the output image depending on the brightness of anenvironment in which the output image is viewed, the color tone of alight source for viewing, or the like, and desirable reproduction ofcolors of the output image depending on the application of the outputimage or the like, for example, reproduction of colors desirable forviewing, which is not reproduction of colors of actual objects such asblue of sky or green of trees but reproduction of colors depending onviewing targets such as movies, televisions (TV), indoor advertisements,and outdoor advertisements.

That is, as illustrated in FIG. 3A, the RRT 32 performs renderingtransform f on the image data DeSat(RGBi(Ri, Gi, Bi)) in the ACES colorspace 28 of which the chroma has decreased by the chroma decreaseprocessing unit 30 according to the following Expression (3) totransform the image data into image data RGBo(Ro, Go, Bo) in the OCEScolor space.

RGBo=f(DeSat(RGBi))  (3)

Next, similarly to the ODT 138 illustrated in FIG. 12, the ODT 34performs color space transform or gamma (γ value) transform orcalibration of the display device 22 and sends the output image 38 asthe output image data to the display device 22. That is, the ODT 34transforms the output standard color space that is independent from theoutput device into the output device color space that is dependent onthe display device 22 as an actual output device, andoutput-device-transforms the image data in the output standard colorspace into the output image data for display on the display device 22 asan output device.

In the output transform unit 20 according to this embodiment, threeprocessings of the chroma decrease processing by the chroma decreaseprocessing unit 30, the transform into the OCES color space by the RRT32, and the output device transform by the ODT 34 are performed assingle processing using a single 3DLUT, but since the input values ofthe 3DLUT are image data in the ACES color space 28 of which the chromahas been increased by the chroma increase processing unit 16 and thegrid points can be taken in an area other than a portion having highchroma, points in the input color space and fine color densities(brightness, hue, and chroma) which are present in a scene can bereproduced in the output color space with high accuracy.

The display device 22 receives the output image data in the outputdevice color space, that is, the color space of the display device 22,output from the output transform unit 20, and outputs the receivedoutput image data to display the output image on the display screenthereof.

The display device 22 is not particularly limited as long as it is anoutput device outputting the output image, and, for example, a digitalprojector, a motion picture projector, a TV, and various image monitorswith a large size to a small size which can output a video as the outputimage can be used.

Thus, in the image processing apparatus 10 according to this embodiment,it is possible to increase the density of the grid points in thevicinity of gray without increasing the number of grid points of the3DLUT, and thus, it is possible to improve the accuracy of the colorspace transform of image data with a color space of a wide dynamic rangeusing a three-dimensional lookup table.

The image processing apparatus according to the first embodimentbasically has the above-mentioned configuration.

The operations of the image processing apparatus according to theinvention and the image processing method according to the inventionwill be described below.

FIG. 4 is a flowchart illustrating an example of a process flow of theimage processing method according to the invention.

As illustrated in FIG. 4, in step S10, image data of a camera image 24is input to the data input unit 12 of the image processing apparatus 10illustrated in FIG. 2 and is acquired in the image processing apparatus10.

Then, in step S12, the camera image data is transformed into image datain the ACES color space 28 which is a common input color space by theIDT 26 of the input transform unit 14.

Subsequently, in step S14, processing of increasing the chroma isperformed on the image data in the ACES color space 28 by the chromaincrease processing unit 16.

Then, in step S16, color adjustment processing is performed on thechroma-increased image data in the ACES color space 28 by the coloradjusting unit 18.

Then, in steps S18 to S22, output transform processing is performed onthe color-adjusted chroma-increased image data by the output transformunit 20.

First, in step S18 of the output transform, processing of decreasing thechroma of the color-adjusted chroma-increased image data (image data inthe ACES color space 28) to return the chroma to the original chroma isperformed by the chroma decrease processing unit 30 of the outputtransform unit 20.

Then, in step S20 of the output transform, the color-adjustedchroma-increased (returned) image data (the image data in the ACES colorspace 28) is subjected to the rendering transform and is transformedinto image data in the output standard color space (for example, theOCES color space) by the RRT 32 of the output transform unit 20.

Subsequently, in step S22 of the output transform, the image data in theoutput standard color space (the OCES color space) is transformed intooutput-device-referred image data in the color space of the outputdevice (the display device 22) by the ODT 34 of the output transformunit 20.

The chroma decrease processing, the rendering transform, and the outputdevice transform of steps S18 to S22 are preferably performed as asingle output transform processing using a single 3DLUT by the outputtransform unit 20.

Then, in step S24, the output-device-referred image data obtained inthis way is displayed as an output image on the display screen of thedisplay device 22 as the output device.

Thus, in the image processing method according to this embodiment, byincreasing the chroma of image data and inputting the resultant imagedata to the 3DLUT, it is possible to efficiently use a 3DLUT withoutincreasing the number of grid points of the 3DLUT. As a result, it ispossible to increase the density of the grid points in the vicinity ofgray, and thus, it is possible to improve the accuracy of the colorspace transform of image data with a color space of a wide dynamic rangeusing a three-dimensional lookup table.

Therefore, the output image displayed on the display device 22 is animage in which color, chroma, and brightness are reproduced accuratelyeven in fine portions and is an image preferably reproduced.

The image processing method according to this embodiment basically hasthe above-mentioned configuration.

In the above-mentioned image processing apparatus and the imageprocessing method according to the first embodiment, the respectiveprocessings in the chroma decrease processing unit 30, the RRT 32, andthe ODT 34 of the output transform unit 20 are performed as a singleoutput transform processing using a single 3DLUT, but the invention isnot limited to this. Two or more of these processings may be performedusing a single 3DLUT, or may be performed without using a 3DLUT, or oneor two of these processings may be performed using a 3DLUT and the otherprocessings may be performed without using a 3DLUT.

For example, the image processing method or the image processingapparatus according to the invention can be applied to a video check andcolor adjustment system in which at a filming location, a captured imageis transformed and displayed on a display monitor for video check andfurther, color adjustment is performed by the color adjusting unit 18illustrated in FIG. 2. Here, the color adjustment result at the filminglocation can be transferred to post-process of video editing as a 3DLUT.At this time, it is necessary to divide the 3DLUT into a 3DLUT for inputtransform including the color adjustment result and a 3DLUT for outputtransform so that additional color adjustment in the ACES color spacecan be performed in the post-process. Since most of the post-processsystems use only the transform in the 3DLUT, it is preferable to use theimage processing method or the image processing apparatus of theinvention using the ACES color space in which the chroma is emphasized.

Furthermore, in order to ensure uniformity of colors between systems, itis preferable that the image processing of the invention be used in asystem not using a 3DLUT, for example, a system capable of directlycalculating the operation expression of the RRT.

Next, a second embodiment of the invention will be described below.

FIG. 5 is a block diagram schematically illustrating a second embodimentof the configuration of the image processing apparatus that performs theimage processing method according to the invention.

The image processing apparatus 90 illustrated in the drawing includes ahigh-chroma color space transform unit 92 and a high-chroma color spaceinverse transform unit 94 instead of the chroma increase processing unit16 and the chroma decrease processing unit 30 in the image processingapparatus 10 according to the first embodiment illustrated in FIG. 2.

The other elements of the image processing apparatus 90 according tothis embodiment are the same as in the image processing apparatus 10according to the first embodiment and thus description thereof will notbe repeated.

The high-chroma color space transform unit 92 is an example of thechroma/chromaticity optimizing unit 84 illustrated in FIG. 1. After theinput transform by the input transform unit 14, the high-chroma colorspace transform unit 92 performs transform processing of transforminginput image data in an input color space (for example, ACES color space28) into image data in a high-chroma color space in which chroma hasbeen increased with respect to the input color space to acquiretransformed image data, as illustrated in FIG. 2.

As described above, the input image data in the input color space ishardly present in a high-chroma area, that is, an area in which thechroma is higher than a predetermined value.

Accordingly, by transforming the input image data in the input colorspace into the image data in the high-chroma color space through the useof the high-chroma color space transform unit 92 and applying a 3DLUThaving the same number of grid points as the conventional 3DLUT definedto cover the input color space to a central area of the high-chromacolor space, that is, an area in which the input image data is actuallypresent, it is possible to increase the chroma of the input image datain the input color space and to input the resultant input image data tothe 3DLUT, similarly to the chroma increase processing unit 16 of theimage processing apparatus 10 according to the first embodiment.

In the output transform, the high-chroma color space inverse transformunit 94 performs image processing of transforming the transformed imagedata into the output image data using a 3DLUT including inversetransform processing of inversely transforming the transformed imagedata in the high-chroma color space into the input image data in theinput color space.

Thus, similarly to the chroma decrease processing unit 30 of the imageprocessing apparatus 10 according to the first embodiment, it ispossible to transform the transformed image data to the output imagedata by decreasing the chroma of the transformed image data by theamount of chroma increased and returning the chroma to the chroma of theinput image data.

As described above, in the image processing apparatus 90 according tothe second embodiment, since the chroma of the input image data can beincreased and then the resultant input image data can be input to the3DLUT, the same effects as in the image processing apparatus 10according to the first embodiment can be obtained.

Next, a third embodiment of the invention will be described below.

FIG. 6 is a block diagram schematically illustrating a third embodimentof the configuration of the image processing apparatus that performs theimage processing method according to the invention.

The image processing apparatus 100 illustrated in the drawing includes alow-chromaticity color space transform unit 102 and a low-chromaticitycolor space inverse transform unit 104 instead of the chroma increaseprocessing unit 16 and the chroma decrease processing unit 30 in theimage processing apparatus 10 according to the first embodimentillustrated in FIG. 2.

The other elements of the image processing apparatus 100 according tothis embodiment are the same as in the image processing apparatus 10according to the first embodiment and thus description thereof will notbe repeated.

The low-chromaticity color space transform unit 102 is an example of thechroma/chromaticity optimizing unit 84 illustrated in FIG. 1. After theinput transform by the input transform unit 14, the low-chromaticitycolor space transform unit 102 performs transform processing oftransforming input image data in an input color space, for example,input image data in an RGB color space, into image data in a first colorspace composed of brightness and chromaticity, such as a Ycbcr colorspace and an L*a*b* color space, and further transforming the firstcolor space into a low-chromaticity color space in which thechromaticity of the first color space has decreased to acquiretransformed image data.

FIG. 7 is a conceptual diagram illustrating a state of transforming thefirst color space composed of brightness and chromaticity into thelow-chromaticity color space in which the chromaticity of the firstcolor space has decreased.

As illustrated on the left side of the drawing, the first color space isa color space composed of an axis of brightness and two axes ofchromaticities a and b. Image data in the first color space is presentin an area which extends from a low-brightness area to a high-brightnessarea and in which two chromaticities a and b extend in an ellipticalshape with the center of brightness as a peak. That is, the image datain the first color space is hardly present in a high-chromaticity areain which each of two chromaticities a and b is higher than apredetermined value.

As illustrated on the right side of the drawing, the low-chromaticitycolor space transform unit 102 transforms coordinates of twochromaticities a and b in the first color space into a low-chromaticitycolor space in which two chromaticities a and b of the first color spacehave decreased so as to remove a high-chromaticity area where the imagedata in the first color space is hardly present and each of twochromaticities a and b is higher than a predetermined value. Thus, thedifference between a space of two chromaticities a and b in thelow-chromaticity color space and a space of two chromaticities a and bof the image data in the first color space can be reduced so that thespace of two chromaticities a and b in the low-chromaticity color spacecan effectively use the space of two chromaticities a and b of the imagedata in the first color space.

Accordingly, by transforming the first color space into thelow-chromaticity color space through the use of the low-chromaticitycolor space transform unit 102 and applying a 3DLUT having the samenumber of grid points as the conventional 3DLUT defined to cover theentire area of the input color space to an area of the low-chromaticitycolor space, that is, an area in which the input image data is actuallypresent, it is possible to increase the chromaticity of the image datain the first color space and to input the resultant image data to the3DLUT, similarly to the chroma increase processing unit 16 of the imageprocessing apparatus 10 according to the first embodiment.

In the output transform, the low-chromaticity color space inversetransform unit 104 performs image processing of transforming thetransformed image data to the output image data using a 3DLUT includinginverse transform processing of inversely transforming thelow-chromaticity color space to the first color space and inverselytransforming the image data in the inversely-transformed first colorspace to the input image data in the input color space.

Thus, similarly to the chroma decrease processing unit 30 of the imageprocessing apparatus 10 according to the first embodiment, it ispossible to transform the transformed image data into the output imagedata by decreasing the chromaticity of the transformed image data by theamount of chromaticity increased and returning the chromaticity to thechromaticity of the input image data.

As described above, in the image processing apparatus 100 according tothe third embodiment, since the chromaticity of the input image data canbe increased and then the resultant input image data can be input to the3DLUT, the same effects as in the image processing apparatus 10according to the first embodiment can be obtained.

Next, a fourth embodiment of the invention will be described below.

FIG. 8 is a block diagram schematically illustrating a fourth embodimentof the configuration of the image processing apparatus that performs theimage processing method according to the invention.

The image processing apparatus 110 illustrated in the drawing includes alow-chroma color space transform unit 112 and a low-chroma color spaceinverse transform unit 114 instead of the low-chromaticity color spacetransform unit 102 and the low-chromaticity color space inversetransform unit 104 in the image processing apparatus 100 according tothe third embodiment illustrated in FIG. 6.

The other elements of the image processing apparatus 110 according tothis embodiment are the same as in the image processing apparatus 100according to the third embodiment and thus description thereof will notbe repeated.

The low-chroma color space transform unit 112 is an example of thechroma/chromaticity optimizing unit 84 illustrated in FIG. 1. After theinput transform by the input transform unit 14, the low-chroma colorspace transform unit 112 performs transform processing of transforminginput image data in an input color space, for example, input image datain an RGB color space, into image data in a second color space composedof brightness, chromaticity, and hue, such as an L*C*H* color space andan HSL color space, and further transforming the second color space intoa low-chroma color space in which the chroma of the second color spacehas decreased to acquire transformed image data.

FIG. 9 is a conceptual diagram illustrating a state of transforming thesecond color space composed of brightness, chromaticity, and hue intothe low-chroma color space in which the chroma of the second color spacehas decreased.

As illustrated on the left side of the drawing, the second color spaceis a color space composed of an axis of brightness, an axis ofchromaticity, and an axis of hue. Image data in the second color spaceis present in an area which extends from a low-brightness area to ahigh-brightness area, which extends from a low-hue area to a high-huearea, and in which the chroma extends in an elliptical shape with thecenter of brightness as a peak. That is, the image data in the secondcolor space is hardly present in a high-chroma area in which the chromais higher than a predetermined value.

As illustrated on the right side of the drawing, the low-chroma colorspace transform unit 112 transforms the coordinate of the chroma of thesecond color space into a low-chroma color space in which the chroma ofthe second color space has decreased so as to remove a high-chroma areain which the image data in the second color space is hardly present andthe chroma is higher than a predetermined value. Thus, the differencebetween both spaces of the chroma can be reduced so that the space ofthe chroma in the low-chroma color space can effectively use the spaceof the chroma of the image data in the second color space.

Accordingly, by transforming the second color space into the low-chromacolor space through the use of the low-chroma color space transform unit112 and applying a 3DLUT having the same number of grid points as theconventional 3DLUT defined to cover the entire input color space to anarea of the low-chroma color space, that is, an area in which the inputimage data is actually present, it is possible to increase the chroma ofthe image data in the second color space and to input the resultantimage data to the 3DLUT, similarly to the chroma increase processingunit 16 of the image processing apparatus 10 according to the firstembodiment.

In the output transform, the low-chroma color space inverse transformunit 114 performs image processing of transforming the transformed imagedata into the output image data using a 3DLUT including inversetransform processing of inversely transforming the low-chroma colorspace into the second color space and inversely transforming the imagedata in the inversely-transformed second color space to the input imagedata in the input color space.

Thus, similarly to the chroma decrease processing unit 30 of the imageprocessing apparatus 10 according to the first embodiment, it ispossible to transform the transformed image data into the output imagedata by decreasing the chroma of the transformed image data by theamount of chroma increased and returning the chroma to the chroma of theinput image data.

As described above, in the image processing apparatus 110 according tothe fourth embodiment, since the chroma of the input image data can beincreased and then the resultant input image data can be input to the3DLUT, the same effects as in the image processing apparatus 10according to the first embodiment can be obtained.

A fifth embodiment of the image processing apparatus that performs theimage processing method according to the invention will be describedbelow.

FIG. 10 is a block diagram schematically illustrating a fifth embodimentof the configuration of the image processing apparatus that performs theimage processing method according to the invention.

As illustrated in FIG. 10, the image processing apparatus 50 includes animage transmitting device 52 acquiring an image and transmitting imagedata thereof to an output device and an image display device 54displaying an output image on the basis of the image data transmittedfrom the image transmitting device 52, and constitutes an imagetransmitting system.

The image transmitting device 52 includes an image acquiring unit 56acquiring a camera image 57, an input device transform unit 58transforming image data of the camera image 57 into image data in acommon input color space, for example, an ACES color space of the AMPAS,a chroma increase processing unit 60 increasing the chroma of image datain the common input color space, an integer encoding unit 62integer-encoding the chroma-increased image data, and an imagetransmitting unit 64 transmitting image data compressed through theinteger encoding to the image display device 54.

The image acquiring unit 56, the input device transform unit 58, and thechroma increase processing unit 60 illustrated in FIG. 10 correspond tothe data input unit (image acquiring unit) 12, the input transform unit14, and the chroma increase processing unit 16 of the image processingapparatus 10 illustrated in FIG. 2, respectively, and detaileddescription thereof will not be repeated.

Before transmitting an image through the image transmitting unit 64, theinteger encoding unit 62 compresses the chroma-increased image data inan area in which the high-chroma area is removed from the common inputcolor space. The integer encoding unit 62 is not particularly limited aslong as it can perform known compression encoding.

The image transmitting unit 64 transmits the chroma-increased image datain the common input color space compressed by the integer encoding unit62 to the image display device 54. The image transmitting unit 64 is notparticularly limited as long as it can transmit image data in a knownimage transmission manner.

The image display device 54 includes an image receiving unit 66receiving the chroma-increased image data in the common input colorspace transmitted from the image transmitting device 52, a coloradjusting unit 68 performing color adjustment on the chroma-increasedimage data in the common input color space, a chroma decrease processingunit 70 decreasing the chroma of the color-adjusted chroma-increasedimage data in the common input color space to return the chroma to theoriginal chroma, an output device transform unit 72 transforming thechroma-returned image data in the common input color space intooutput-device-referred image data in the color space of an output device(a display unit 74), and the display unit 74 displaying an output image73 on the basis of the output-device-referred image data. The chromadecrease processing unit 70 and the output device transform unit 72constitutes an output transform unit 76.

In the image processing apparatus 50 according to this embodimentillustrated in FIG. 10, similarly to the image processing apparatus 10illustrated in FIG. 2, the output transform unit 76 constituted by thechroma decrease processing unit 70 and the output device transform unit72 preferably performs processing using a single 3DLUT.

The color adjusting unit 68, the chroma decrease processing unit 70, andthe display unit 74 illustrated in FIG. 10 correspond to the coloradjusting unit 18, the chroma decrease processing unit 30 of the outputtransform unit 20, and the display device 22 of the image processingapparatus 10 illustrated in FIG. 2, respectively, and the output devicetransform unit 72 illustrated in FIG. 10 corresponds to theconfiguration constituted by the RRT 32 and the ODT 34 of the outputtransform unit 20 of the image processing apparatus 10 illustrated inFIG. 2. Accordingly, the output transform unit 76 illustrated in FIG. 10which is constituted by the chroma decrease processing unit 70 and theoutput device transform unit 72 corresponds to the output transform unit20 of the image processing apparatus 10 illustrated in FIG. 2, and thusdetailed description thereof will not be repeated.

The image receiving unit 66 receives compressed image data obtained byinteger-encoding the chroma-increased image data in an area in which ahigh-chroma area of the common input color space is removed and which istransmitted from the image transmitting unit 64 of the imagetransmitting device 52. The image receiving unit 66 is not particularlylimited as long as it is a receiving unit of a known receiving manner.

Also in the image processing apparatus 50 according to this embodimentillustrated in FIG. 10, similarly to the image processing apparatus 10illustrated in FIG. 2, in the output transform unit 76, threeprocessings of the chroma decrease processing by the chroma decreaseprocessing unit 70, the transform into the output standard color spaceby the RRT or the like, and the output device transform by the ODT orthe like are performed as single processing using a single 3DLUT, butsince the input values of the 3DLUT are image data in the common inputcolor space of which the chroma has been increased by the chromaincrease processing unit 60 and the grid points can be taken in an areaother than a portion having high chroma, points in the input color spaceand fine color densities (brightness, hue, and chroma) which are presentin a scene can be reproduced in the output color space with highaccuracy.

Thus, in the image processing apparatus 50 according to this embodiment,by increasing the chroma of the image data and inputting the resultantimage data to the 3DLUT, it is possible to efficiently use the 3DLUT,without increasing the number of grid points of the 3DLUT. Therefore, itis possible to increase the density of the grid points in the vicinityof gray without increasing the number of grid points of the 3DLUT andthus to improve the accuracy of the color space transform of image datawith a color space of a wide dynamic range using a three-dimensionallookup table.

In the invention, the process flow in the image processing apparatusillustrated in FIG. 10 can be implemented as an image processing method.

That is, at the time of performing the integer encoding on the inputimage data, transmitting the integer-encoded image data, andtransforming the transmitted integer-encoded image data into the outputimage data for displaying the output image, the image processing methodaccording to this embodiment can be implemented by performing processingof increasing the chroma before the integer encoding and performinginverse transform processing of decreasing the chroma to return thechroma as preprocessing before displaying the output image.

Accordingly, also in the image processing method according to the fifthembodiment, the same effects as in the image processing apparatus 50according to the fifth embodiment or in the image processing methodaccording to the first embodiment can be obtained.

In the above-mentioned image processing apparatus and the imageprocessing method according to the fifth embodiment, the processings inthe chroma decrease processing unit 70 of the output transform unit 76and in the output device transform unit 72 including the RRT and the ODTare performed as single output transform processing using a single3DLUT, but the invention is not limited to this. Two or more of theseprocessings may be performed using a 3DLUT, or may be performed withoutusing a 3DLUT, or one or two processings may be performed using a 3DLUTand the other processings may be performed without using a 3DLUT.

The application of the image processing apparatus and the imageprocessing method according to the fifth embodiment to the video checkand color adjustment system can be carried out in the same way as in theimage processing method or the image processing apparatus according tothe first embodiment.

The above-mentioned image processing method can be embodied in acomputer by executing an image processing program.

For example, the image processing program according to the inventionincludes sequences causing a computer, specifically, a CPU thereof, toexecute the respective steps of the image processing method. The programincluding these sequences may be constituted as one or more programmodules.

The image processing program including the sequences that are executedby a computer may be stored in a memory (storage unit) of a computer ora server, or may be stored in a recording medium, and is read from thememory or the recording medium by the computer (CPU) or another computerand executed.

Accordingly, the invention may be embodied as a computer-readable memoryor recording medium having the image processing program causing acomputer to execute the image processing method.

Hereinbefore, the image processing method, the image processingapparatus, the image processing program, and the computer-readablerecording medium according to the invention have been described indetail, but the invention is not limited to the above-mentionedembodiments and may be improved or modified in various forms within ascope that does not depart from the gist of the invention.

What is claimed is:
 1. An image processing method comprising: performinginput transform into an input color space, which is independent from aninput device, on input image data of the input device; after the inputtransform, performing transform processing of transforming chroma orchromaticity of the input image data or chroma or chromaticity in theinput color space so as to reduce a difference between a space of chromaor chromaticity of the input image data and a space of chroma orchromaticity in the input color space so that the space of chroma orchromaticity of the input image data effectively uses the space ofchroma or chromaticity in the input color space to acquire transformedimage data; performing integer encoding on the transformed image data;and performing inverse transform processing of returning the chroma orchromaticity of the transformed image data to the chroma or chromaticityof the input image data and image processing of transforming thetransformed image data into an output image data of an output device byperforming output transform into an output color space of the outputdevice on the transformed image data.
 2. The image processing methodaccording to claim 1, wherein after the input transform, transformprocessing of increasing the chroma of the input image data is performedto acquire transformed image data, and in the output transform, inversetransform processing of decreasing an amount of chroma increased in thetransformed image data to return the chroma to the chroma of the inputimage data and image processing of transforming the transformed imagedata into the output image data are performed.
 3. The image processingmethod according to claim 1, wherein after the input transform,transform processing of transforming the input image data in the inputcolor space into image data in a high-chroma color space in which chromahas increased with respect to the input color space is performed toacquire transformed image data and in the output transform, inversetransform processing of inversely transforming the transformed imagedata in the high-chroma color space into the input image data in theinput color space and image processing of transforming theinversely-transformed input image data into the output image data areperformed.
 4. The image processing method according to claim 1, whereinafter the input transform, transform processing of transforming theinput image data in the input color space into image data in a firstcolor space composed of brightness and chromaticity and transforming thefirst color space into a low-chromaticity color space in which thechromaticity of the first color space has decreased is performed toacquire transformed image data and in the output transform, inversetransform processing of inversely transforming the low-chromaticitycolor space into the first color space and inversely transforming theimage data in the inversely-transformed first color space into the inputimage data in the input color space and image processing of transformingthe inversely-transformed input image data into the output image dataare performed.
 5. The image processing method according to claim 1,wherein after the input transform, transform processing of transformingthe input image data in the input color space into image data in asecond color space composed of brightness, chroma, and hue andtransforming the second color space into a low-chroma color space inwhich the chroma of the second color space has decreased is performed toacquire transformed image data, and in the output transform, inversetransform processing of inversely transforming the low-chroma colorspace into the second color space and inversely transforming the imagedata in the inversely-transformed second color space into the inputimage data in the input color space and image processing of transformingthe inversely-transformed input image data into the output image dataare performed.
 6. The image processing method according to claim 1,wherein the output transform performs the inverse transform processingand the image processing using a three-dimensional lookup table.
 7. Theimage processing method according to claim 1, wherein the transformprocessing is performed in a logarithmic color space using the inputimage data and the transform image data which are transformed inlogarithmic values.
 8. The image processing method according to claim 1,wherein the transform processing is performed using a Red, Green, andBlue matrix.
 9. The image processing method according to claim 1,wherein, when the transform processing is performed, a rate of increaseof chroma is changed depending on a distance of the input image datafrom gray in an input color space of the input image data.
 10. An imageprocessing apparatus comprising: an input transform processor whichperforms input transform into an input color space, which is independentfrom an input device, on input image data of the input device; achroma/chromaticity optimizing processor which performs transformprocessing of transforming chroma or chromaticity of the input imagedata or chroma or chromaticity in the input color space so as to reducea difference between a space of chroma or chromaticity of the inputimage data and a space of chroma or chromaticity in the input colorspace so that the space of chroma or chromaticity of the input imagedata effectively uses the space of chroma or chromaticity in the inputcolor space to acquire transformed image data, after the inputtransform; an integer encoding processor which performs integer encodingon the transformed image data acquired by the chroma/chromaticityoptimizing unit; and an output transform processor which performs outputtransform into an output color space of an output device on thetransformed image data subjected to integer encoding by the integerencoding unit to acquire output image data of the output device, whereinin the output transform, the output transform unit performs inversetransform processing of returning the chroma or chromaticity of thetransformed image data to the chroma or chromaticity of the input imagedata and image processing of transforming the transformed image datainto the output image data.
 11. The image processing apparatus accordingto claim 10, wherein, after the input transform, the chroma/chromaticityoptimizing unit performs transform processing of increasing chroma ofthe input image data to acquire transformed image data, and in theoutput transform, the output transform unit performs inverse transformprocessing of decreasing the chroma of the transformed image data by anincreased amount to return the chroma of the transformed image data tothe chroma of the input image data and image processing of transformingthe transformed image data into the output image data.
 12. The imageprocessing apparatus according to claim 10, wherein, after the inputtransform, the chroma/chromaticity optimizing unit performs transformprocessing of transforming the input image data in the input color spaceinto image data in a high-chroma color space in which chroma hasincreased with respect to the input color space to acquire transformedimage data, and in the output transform, the output transform unitperforms inverse transform processing of inversely transforming thetransformed image data in the high-chroma color space into the inputimage data in the input color space and image processing of transformingthe inversely transformed input image data into the output image data.13. The image processing apparatus according to claim 10, wherein, afterthe input transform, the chroma/chromaticity optimizing unit performstransform processing of transforming the input image data in the inputcolor space into image data in a first color space composed ofbrightness and chromaticity and transforming the first color space intoa low-chromaticity color space in which the chromataicity of the firstcolor space has decreased to acquire transformed image data, and in theoutput transform, the output transform unit performs inverse transformprocessing of inversely transforming the low-chromaticity color spaceinto the first color space and image processing of transforming theinversely transformed input image data into the output image data. 14.The image processing apparatus according to claim 10, wherein, after theinput transform, the chroma/chromaticity optimizing unit performstransform processing of transforming the input image data in the inputcolor space into image data in a second color space composed ofbrightness, chroma and hue and transforming the second color space intoa low-chroma color space in which the chroma of the second color spacehas decreased to acquire transformed image data, and in the outputtransform, the output transform unit performs inverse transformprocessing of inversely transforming the low-chroma color space into thesecond color space and inversely transforming image data in theinversely transformed second color space into the input image data inthe input color space and image processing of transforming the inverselytransformed input image data into the output image data.
 15. The imageprocessing apparatus according to claim 10, wherein the output transformunit performs the inverse transform processing and the image processingusing a three-dimensional lookup table.
 16. A non-transitorycomputer-readable recording medium having recorded thereon an imageprocessing program for causing a computer to execute respective steps ofthe image processing method according to claim 1.